Ramp generator a chart recorder

ABSTRACT

A ramp generator for a chart recorder or the like and a chart recorder for permanently recording information on recording media by sampling means for sampling signals is described. The ramp generator generates a ramp signal whose magnitude gradually changes in response to movement of the recording media rather than time. The ramp signal thus derived is applied to a strobe comparator via a slow ramp control circuit as the reference level thereof for producing a strobe pulse to drive the sampling gate and thereby sampling a signal applied thereto.

United States Patent Geerling 1 Oct. 31, 1972 [54] RAMP GENERATOR ACHART 3,175,161 3/1965 l-lackborn et al. 346/33 R RECORDER PrimaryExaminer-Joseph W. l-lartary [72] lnvemor' 3:22:32: gg Gen-lingAttorney-Adrian J. LaRue et al.

[73] Assignee: Tektronix,Inc.,Beaverton,Oreg. [57] TR Filed: June 28,1971 A-ramp generator for a chart recorder or the like and [21] APPL No:153,922 a chart recorder for permanently recording information onrecording media by sampling means for sampling signals is described. Theramp generator "346/33 346/136 2452 generates a ramp signal whosemagnitude gradually e n h g i response t movement f th di g [58] new of512 media rather than time. The ramp signal thus derived I is applied toa strobe comparator via a slow ramp con- 56] R f i C1 d trol circuit asthe reference level thereof for producing e erences I e a strobe pulseto drive the sampling gate and thereby UNITED STATES PATENTS Sampling aSignal app thereto- 2,712,l28 6/1955 Woodruff .;.346/33 R 8 Claims, 5Drawing Figures TRANSMISSION um:

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. TED um 31 1912 INVENTOR Leoumous Johnny; serum us Y ATTORNY' 1 RAMPGENERATOR ACI-IART RECORDER BACKGROUND OF THE INVENTION A from thedigital-to-analog converter. This construction ensures precise measuringaccuracy of the chart recorder.

The present invention relates to a ramp generator for vto provide highfrequency measuring capability by reducing the frequency bandwidth.

In a conventional measuring instrument such as a cathode ray tube'oscilloscope,a strobe comparator-is employed for producing an outputwhen a fast ramp signal applied to one input terminal of the comparatorcoincides with a slow ramp signal or a staircase signal applied to theother input terminal thereof so as to produce samples of the inputsignal each delaying gradually in relation to the occurrence of arepetitive input signal. Ina cathode ray tube oscilloscope, the slowramp signal is also utilized as a horizontal sweep signalfor deflectingthe electron beam of the cathode ray tube. Therefore, there is nopossibility to cause error between the time when signal sampling istaking place and the electron beam position on a phosphor screen of thecathode ray tube.

On the other hand, in a chart recorder wherein the time duration dependson the motor speed for moving the recording'media such, for example, aspaper, an independent slow ramp signal should be generated in order toobtain correct samples. However, the motor speed tends to change duringoperation in accordance with friction, power source, load condition andother SUMMARY OF THE INVENTION According to the present invention, theslow ramp generator is precisely controlled by the movement of therecording media itself throughout the entire movement thereof. That is,there is employed a means for detecting both of the speedand theposition of the recording media. The means may consist of a pulsegenerator for generating pulses of a predetermined duration having arepetition rate directly proportional to the movement of the recordingmedia or the motor, a pulse counter for counting the number of pulsesgenerated by the generator, and a digital-to-analog converter forconverting the output from the pulse counter to an analog signal. Therepetition rate of the pulses produced from the pulse generatorcorresponds to the speed of the recording media. On the other hand,

the output from the digital-to-analog converter represents the'totalmovement of the recording media.

parator is then fed back to the slow ramp generator so that the slowramp generator generates a slow ramp signal having an identical slope asthat of the output It is therefore one object of the present inventionto provide a ramp generatorfor a chart recorder or the like wherein theoutput therefrom precisely follows the movement of the recording media.I

It is another object of the present invention to provide a chartrecorder operated by sampling means for sampling signals. v

It is still another object of the present invention to provide animproved chart recorder including a ramp generator whose output isprecisely controlled by the movement of the recording media.

It is yet another object of the present invention. to provide improvedtime domain reflectometry circuitry which can record the signaltransmission characteristic of a transmission line on the recordingmedia.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. The invention, however, both as to organization anddescription of operation, together with further advantages and objectsthereof, may best be understood by reference to the followingdescription takenin connection with the ac,- companying drawings whereinlike reference characters refer to like elements.

BRIEF DESCRIPTION THE DRAWINGS FIG. 1 is a block diagram of oneembodiment of a chart recorder according to the present invention;

FIG. 2 is a detailed block diagram of theslow ramp generator andthe'recording media driving circuit in FIG. 1; FIG. 3 is a perspectiveview of a recording mechanism of one embodiment of the present inventionand also illustrating another embodiment for deriving pulsescorresponding to the movement of the recording media;

. FIG. 4 is a graph of waveforms illustrating the operation of thepresent invention; and

FIG. 5 is a graph of waveforms forexplaining the operation of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1illustrating a block diagram of one embodiment of the present inventionapplied to time domain refiectometry for measuring signal propagationcharacteristics of a high frequency transmission line, a transientresponse of an electronic apparatus and so on, a device 10 represents,for example, a coaxial cable for transmitting television signals, whichI is to be tested. The characteristics of the coaxial cable 10 will berecorded on a recording media 12, for instance, made of a paper having apluralty of a parallel horizontal and vertical lines respectivelyprinted thereon and thereby defining a chart. A circuit 14 represents animportant portion of the present inven-.

tion including a driving mechanism 16 for driving the recording media 12and a slow ramp generator 18 for generating a slow ramp signal 19synchronized with the movement of the recording media 12, details ofwhich will be described hereinafter when referring to FIG. 2. A motorcontrol circuit 20 controls the operation of the a driving mechanism 16and the other circuits, whichis described and claimed in copending US.Pat. application, Ser. No. 158,923 filed June 28, 1971 by the sameinventor and assigned to the present assignee.

A fast ramp generator 22 generally defining a capacitor and a constantcurrent source generates a fast ramp signal 23 having a faster slopethan the slow signal 19 from the slow ramp generator 18. The fast rampgenerator 22 may be triggered by an astable multivibrator. A slow rampcontrol circuit 24 controls the amplitude and dc offset level of theslow ramp signal 19. A strobe comparator 26 receives the fast rampsignal 23 and the slow ramp signal 25 from the slow ramp control circuit24. The strobe comparator 26 produces an output signal when the fastramp signal 23 exceeds the reference lever or the slow ramp signal 25.The amplitude of the slow ramp signal 19 is selected to be-the same asthat of the fast ramp signal 23, however that of the slow ramp signal 25may be attenuated selectably, for example, by the factor of 2.5, 10, 25,100 and 250.

Moreover, the dc level of the slow ramp signal 25 may be adjusted to anylevel within the minimum and maximum value of the fast ramp signal 23 byselecting the 'means transmits a sample pulse 33 to a memory 34.

Pulse 33 has a magnitude corresponding to that of the input signal atthe instance when the sampling gate 33 is driven to open by the strobepulse 31. The memory 34. generally including a capacitor, stores thepeak value of the sample 33 until the next sample is taken.

The signal 35 stored in the memory 34 is then amplified to a sufficientmagnitude by a conventional amplifier 36 so that the pen motor 38records the input information on the recording media 12. Subsequentsampling signal 35 will drive the pen motor 36 to record a succeedingline according to the magnitude'of the sampling signal 35 therebyrecording a waveform representative of the signal being sampled. V

A pulse generator 40 generates a pulse 41 in synchronism with thegeneration of the fast ramp signal 23. The pulse generator 40 may be ofconventional comparator configuration to produce the pulse 41 when thefast ramp signal 23 exceeds a predetermined value in order to avoidtiming nonlinearity, due to the nonlinearity of the fast ramp signal 23at the leading edge thereof. The output 41 from the pulse generator 40is then applied to a pulse selector 42 which includes a switchingcircuit to impress repetitive impulse signal 45 from an impulsegenerator 44 or step function signal 47 from a step function generator46 to the coaxial cable 10.

As the reference level or the slow ramp signal 25 aptervals in relationto the occurrence ofthe fast ramp .by the following expression:

signal 23, the-impulse signal 45 and the step function signal 47.Accordingly, the signal propogation characteristics of the coaxial cable10 will be recorded on the recording media 12. If there isadiscontinuity in the characteristic impedance somewhere along thecoaxial cable 10, signal reflection from the point will be recorded onthe recording media 12. The time difference on the chart paper or therecording media 12 between the application of the repetitive inputsignal 45 or 47 to the coaxial cable 10 and the receipt of the reflectedsignal is equivalent to twice as long as the time interval forelectricity propagating from the input end of the coaxial cable 10 tothe point causing the signal reflection. The propagation-speed'of.electricity in meters per second along a transmission line is VP ifWhere, Vp propagation speed; C speed of light and F dielectric constant.

Assuming that the time interval on the chart paper 12 between theaforementioned two points is T, the location of the discontinuity or thedistance L thereof in meters. from the input end of the coaxial cable 10will be given by the following expression:

Therefore the defective location of the coaxial cable 10 will bedirectly proportional to the time T, and the horizontal axis may bescaled by the length of the coaxial cable 10 rather than taking intoconsideration the dielectric constant of the insulative material of thecoaxial cable 10. The compensation for a different insulative materialcan be made by adjusting the gain of the slow ramp control circuit 24.

FIG. 2 illustrates a block diagram of the circuit 14 of FIG. 1, and thedescription of the operation of the slow ramp generator 18 will be givenin greater detail. A motor 16, which is preferably dc, is employed todrive the recording media 12 in FIG. 1, and it is controlled by motorcontrol circuit 20. A start switch 50 energizes the motor 16 for movingthe recording media 12. A cam 52 coupled to the motor 16 actuates apulsegenerator 54 comprising, for example, a microswitch connectedbetween a suitable voltage source 56 and a pulse normalizer 58. Thepulse normalizer 58 may be a monostable multivibrator for producingpulses 59 having a fixed pulse width, for example, 10 ms upon receivingthe pulse.55. The can 52 may be formed either with equally-spacedhollows or projections provided on a surface of a wheel. A pulse counter60 consists of a plurality of binary counter stages for counting thenumber p of input pulses. The pulse counter 60 has the capability tocount at least the number of points for calibrating the slow ramp signal19. In the case of fifty calibrating points, the pulse counter 60 mayhave six binary counter stages. The motor control circuit 20 alsosupplies a reset signal to the pulse counter 60 through a control line62 whenever the start switch 50 is closed to counter 60 counts apredetermined number, for example, 60.

given signal from the error comparator, which is explained hereinafterin greater detail in-conjunetion-with FIG. 5, is amplified by an erroramplifier 68 and stored in a memory capacitor 72 through a switchingcircuit 70. The switching circuit 70 isnormally a'transistor and it isopen, however it closes when it receives the pulse 59 from the pulsenormalizer 58 through a control line 69 only forthe short timecorresponding to the pulse width thereof.

Another switching circuit 74, which is similar to switching circuit 70,is connected in parallel with the memory capacitor 72 and it is normallyclosed, however it opens when the ramp generator 18 produces the outputslow ramp signal 19. The switching circuit 74 is controlled by the motorcontrol circuit 20 through a control line 75. An output signal from thememory capacitor 72 is supplied to the slow ramp generator 18 through aninput resistor 76. Another input 80, which may be a constant voltagesource, is also supplied to the slow ramp generator 18 through anotherinput resistor 78. The common junction of the resistors 76 and 78 isconnected to an input terminal of the slow ramp generator 18, which maybe a miller integrator consisting of a high gain amplifier 82 and acapacitor 84 connected between the input and output terminals of theamplifier'82. The slow ramp generator 18 produces an output signalproportional to the integration of the signals applied to the inputterminal of the amplifier 82 via the input resistors 76 and 78 at thetime constant substantially determined by the capacitor 84 and the.resistor 76 and by the capacitor 84 and the resistor 78, respectively.

The input resistor 78 is preferably a variable resistor which can beadjusted so that the error signal 67 from output signal 65 from thedigital-to-analog converter As mentioned above, the slow ramp signal 19having a predetermined maximum amplitude is coupled to the inputterminal of the error comparator 66 through'a conductor 85. A switchingcircuit 86, which maybe either a conventional electronic switchor amechanical switch, is connected across the capacitor 84. By a controlsignal from the motor control circuit 20 via a control line 87, theswitching circuit 86 is normally open when the slow ramp generator 18generates the slow ramp signal 19. On the other hand, the switchingcircuit 86is closed to shunt the capacitor 84 when the slow rampgenerator 18 does not generate the slow ramp signal 19.

Although a more detailed description will be made hereinafter referringto FIGS. 4 and 5, the slow ramp generator 18 precisely follows themovement of the recording media 12 because of the feedback loopcomprising the slow ramp generator 18, the error comparator 66, theerror amplifier 68, the memory capacitor 72 and the input resistor 76.The slow ramp signal 19 at the output terminal 88 of the slow rampgenerator 18 is applied to the slow ramp control circuit 24'.

FIG. 3 illustrates a recording'mechanism of the present invention andalso anothefiembodiment of deriving pulses proportional to the movementof the paper 12. The paper 12 is fed from a paper roll loosely mountedin a cabinet (not shown) of the recording mechanism. The paper 12' isinserted between a pinch roller 106 and a driving roller 104 which iscoupled to the motor 16 via, for example, a conventional belt 102 sothat the paper 12 will be moved. The driving roller 104 is preferablycovered by elastic material, such as rubber, to prevent slipping of thepaper 12. Rollers 108, and 112' are provided between the paper roll 100.and the paper driving mechanism so that the optimum graph will beobtained. The paper 12 is a conventional heat sensitive paper havingvertical 1 14 and horizontal 115 lines, each represents a signalmagnitude and time duration or length of the coaxial cable 10,respectively. A plurality of holes 116 are provided at least at one sideof the paper 12, for example, corresponding to each horizontal line 115.As the time interval or the length is usually measured in reference tothe horizontal lines 115, the calibration points should preferably beselected relative thereto. I

A conventional switch mechanism consisting of a fixed contact 1118; anda movable contact is disposed alongthe holes 116. This switch 118 and120 may be used as a switch for the pulse generator 54 in FIG. 2 andproduces a pulse train as the paper 12 moves in the horizontaldirection.

The pen motor 38 includes a movable arm 122 having, for example, a heatstylus 124 at the end thereof. The heat stylus 124 contacts on the heatsensitive paper 12 just at the portion bent over on the surface of thesmall roller 112. A box 126 represents electrical circuits, such as apen movement amplifier, an on-off motor control circuit, a power supplyfor the heat stylus 124 and an interconnecting device between therecording mechanism and the mainframe of the .chart recorder. The numberof samples taken by the sampling gate 32 in a second or equivalent toseveral centimeters of the paper 12 may be selected by adjusting therepetition rate of the fast ramp signal 23, and typically the number ofsamples is as large as 12,000.

The entire recording mechanism illustrated in FIG. 3 may be providedwithin a cabinet as a plug-in unit which can be selectably inserted intoa plug-in unit compartment in the mainframe of the chart recorder.

Although it is not shown in FIG. 3, the front and the top panels of, therecording unit may be unitary and mounted by hinge means so that theycan be selectably opened to supply or replace the paper roll 100 whennecessary. In this case, the pinch roller 106, the roller 110 and themovable switch contact 120 may be mounted in the movable cover memberfor convenience of operation.

FIGS. 4 and 5 are views of a graph of waveforms illustrating theoperation of the slow ramp generator 18 and the error comparator 66,respectively. The horizontal axis represents time, while the verticalaxis represents voltage. When the startswitch 50 is operated at the timeto, the digital-to-analog converter 64 produces the analog staircasesignal 65. The staircase signal 65 steps a predetermined incrementalamount when the pulse counter 60 receives the pulse 59 from the pulsenormalizer 58 and changes the magnitude as a linear function of themovement of the paper 12'. However, the motor speed is frequentlynonlinear in relation to time because of the static friction of themoving portion of the motor 16, variation of the power source and paperslipperage.

, Assuming that the motor 16 operates at the normal speed during duringthe time to t1, at a slower speed than the normal motor speed during thetime t1-t2 and at a faster speed than the normal motor speed during thetime t2-t3, a curve 65 shows an output staircase signal from thedigital-to-analog converter 64. A line- 130 showsa slow ramp signal atthe terminal 88 of the slow ramp generator 18 at an ideal condition whenthe error signal 67 from the error comparator 66 is always zero orprovides a predetermined normal value.

. Referring to FIG. whose horizontal and vertical axes are magnifiedrelative-to FIG. 4 to illustrate the operation of the error comparator66 more clearly, a

the error comparator 66 is the staircase 65 and the .ramp signal 19'will follow the ideal line 130 during the time t0-t1 as illustrated inFIG. 4. When the motor speed is slower than the normal motor speed, therepetition rate of the pulse 59 b is slower than that of 59a and theerror signal from the error comparator 66 will assume the formillustrated by waveform 67b in FIG. 5. This causes an error signal 132bto cause the charging rate of the capacitor 84 of the slow rampgenerator 18 to decrease to follow the slope of the staircase signal65'. As the error signal 132b is applied to the input terminal of theslow ramp generator 18 through the input resistor 76, the error signal13% will be reduced gradually and the slow ramp signal 19 follows thestaircase signal 65'. Similarly, an error signal 1320 stored in thecapacitor 72 increases the charging rate of the capacitor 84 when themotor speed exceeds the normal motor speed during the time t2-t3.

The slow ramp signal 19' thus derived is applied to the strobecomparator 26 via the slow ramp control circuit 24 as the referencesignal thereof in order to obtain strobe pulses 31.. By adjusting theamplitude and the dc offset level of the slow ramp signal 19, signalsfrom any desired portions of the coaxial cable 10 can be recorded on thepaper 12. As electricity propagates in the transmission lien at enormousspeed, only a slight nonlinearity in time of the slow ramp signal 19causesa great error in the location of the discontinuity of thetransmission line when utilized in a measuring instrument of FIG. 1.However, according to the present invention, the slow ramp signal 19 iscorrectly following the movement of the recording media 12 to eliminatesuch error. Moreover, differing from a screen of a cathode ray tubeoscilloscope, the recording media 12 may be selected long enough torecord reflections from a plurality of discontinuities. This ensures thecon venient and accurate measurement of the input information. Thelarger the number of calibrating points of the slow ramp generator 18with the output from the digital-to-analog converter 64, the moreprecisely the slow ramp signal 19 follows'the staircase signal 65. I

Although the above description covers preferred embodiments of thepresent invention, it will be apparent to those skilled in the art thatmany changes and modifications may be made without departing from thesubject matter thereof. For instance, this invention may be utilized forany kinds of chart recorder or the like, for example a spectrumanalyzer, wherein signals corresponding to the movement of the recordingmedia or the driving means are necessary. The recording means may be aconventional pen andink.

What is claimed is: v

1. A ramp generator for a chart recorder or the like for producing aramp signal which is proportional to movement of a recording media,comprising: V

integrator means for integrating an input signal applied to an inputthereof and for producing said ramp signal, driving means for drivingsaid recording media, detecting means for detecting the speed ofrecording media, converter means for producing an analog signalequivalent to the detection of said detecting means, comparator meansfor comparing outputs from said integrator means and said convertermeans, and

feedback means for applying an output error signal from said comparatormeans to said input of said integrator means for controlling the inputsignal thereto.

2. A ramp generator for a chart recorder or the like according to claim1 wherein said detecting means includes a pulse generator for producingpulses according to the movement of recording media, and said convertermeans includes a pulse counter for counting said pulses and adigital-to-analog converter for converting output from said pulsecounter to an analog signal.

3. A ramp generator for a chart recorder or the like according to claim2 wherein said pulse generator includes switching means actuated in thedetection of holes provided at a side of recording media.

4. A ramp generator for a chart recorder or the like according to claim2 wherein said pulse generator includes switch means for producingpulses in response to the revolution of said driving means.

5. A ramp generator for a chart recorder or the like according to claim3 wherein said holes are provided in said recording media correspondingto horizontal lines thereof. I

6 A chart recorder for recording information on a recording media bysampling means for sampling signals, comprising:

recording media, 7

driving means for moving said recording media,

a-slow ramp generator for producing a slow ramp 6 signal whose amplitudeis proportional to the movement of said recording media, 1

a fast ramp generator for producing a fast ramp signal,

comparator means for receiving said slow and fast ramp signals forproducing an output signal when said slow and said fast ramp signalscoincide with each other,

signal sampling means for providingsamples of input information inresponse to said output signal from said comparator means, and

recording means for recording'said samples of input

1. A ramp generator for a chart recorder or the like for producing aramp signal which is proportional to movement of a recording media,comprising: integrator means for integrating an input signal applied toan input thereof and for producing said ramp signal, driving means fordriving said recording media, detecting means for detecting the speed ofrecording media, converter means for producing an analog signalequivalent to the detection of said detecting means, comparator meansfor comparing outputs from said integrator means and said convertermeans, and feedback means for applying an output error signal from saidcomparator means to said input of said integrator means for controllingthe input signal thereto.
 2. A ramp generator for a chart recorder orthe like according to claim 1 wherein said detecting means includes apulse generator for producing pulses according to the movement ofrecording media, and said converter means includes a pulse counter forcounting said pulses and a digital-to-analog converter for convertingoutput from said pulse counter to an analog signal.
 3. A ramp generatorfor a chart recorder or the like according to claim 2 wherein said pulsegenerator includes switching means actuated in the detection of holesprovided at a side of recording media.
 4. A ramp generator for a chartrecorder or the like according to claim 2 wherein said pulse generatorincludes switch means for producing pulses in response to the revolutionof said driving means.
 5. A ramp generator for a chart recorder or thelike according to claim 3 wherein said holes are provided in saidrecording media corresponding to horizontal lines thereof.
 6. A chartrecorder for recording information on a recording media by samplingmeans for sampling signals, comprising: recording media, driving meansfor moving said recording media, a slow ramp generator for producing aslow ramp signal whose amplitude is proportional to the movement of saidrecording media, a fast ramp generator for producing a fast ramp signal,comparator means for receiving said slow and fast ramp signals forproducing an output signal when said slow and said fast ramp signalscoincide with each other, signal sampling means for providing samples ofinput information in response to said output signal from said comparatormeans, and recording means for recording said samples of inputinformation on said recording media in accordance with the magnitude ofthe samples of input information.
 7. A chart recorder according to claim6 wherein a repetitive impulse signal is applied to a transmission lineunder test and the signal propagation characteristics of saidtransmission line is sampled and recorded on said recording media.
 8. Achart recorder according to claim 6 wherein said recording meansincludes a recording pen driven in orthogonal direction to the movementof said recording media.